This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-228064, filed Jul. 27, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical head and an optical disk apparatus for recording or reproducing information on an optical disk in which a sphere aberration correcting method is particularly improved.
2. Description of the Related Art
There have been techniques for correcting sphere aberration generated on the optical head due to a thickness error of an optical disk substrate so that a utility efficiency of light is improved. This sort of technique is disclosed in, for example, Japanese Patent Application KOKAI Publication Nos. 11-259906, 11-195229, 06-215407, and 11-259894.
The sphere aberration correcting methods according to the conventional techniques are realized by moving a relay lens. However, in these years where information recorded on a disk has been densified refining a beam spot, the techniques that corrects the sphere aberration by only moving the relay lens become insufficient and more improvement has been expected.
Here, an object of the embodiments are to provide an optical head and an optical disk apparatus in which, by adding a limitation to a structure of a relay lens and an objective lens, even when the relay lens is moved in order to correct sphere aberration generated due to a thickness error of an optical disk substrate, a beam diameter being incident on an objective lens does not change.
In order to attain this object, an embodiment comprises a laser light source for outputting a light beam, an optical disk having a recording/reproducing surface and a transparent substrate on the surface, an objective lens for gathering the light beam to the optical disk, a relay lens system comprising one or more lenses inserted between the laser light source and the objective lens, means for moving one or more lenses in the relay lens system toward its optical axis so as to correct the sphere aberration in accordance with a thickness of the transparent substrate of the optical disk, and means for sustaining a diameter of the incident light on the objective lens when one or more lenses in the relay lens system are moved.
Additional objects and advantages will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.